Exploring the potential for enhancing the thermoelectric properties of barium titanate-based materials through the B-site-specific doping and nominal A-site deficiency

This study explores the potential for enhancing the thermoelectric performance of barium titanate through simultaneous Ta doping at the B-site and introducing barium deficiency, under various sintering conditions. The Taguchi method was employed to systematically assess the impacts of doping level, A-site stoichiometry, and sintering temperature on the thermoelectric properties using an L 9 (27) orthogonal array, reducing the number of experiments to 9. XRD and SEM/EDS studies confirmed that the Ta-substituted BaTiO 3 samples are nearly single phase in terms of composition, with only minor traces of TiO 2 detected. The coexistence of cubic and tetragonal symmetries observed in the XRD patterns reflects structural polymorphism within the perovskite phase, rather than the presence of multiple chemical phases. The results demonstrate that Ta substitution at the Ti-site significantly improves electrical conductivity, reaching nearly 40 S/cm at 900 °C with 0.10 mole Ta doping. The lowest thermal conductivity of 1.05 W/m/K was observed for BaTi 0.9 Ta 0.1 O 3 , which represents the best value reported in the literature. This sample also exhibited the highest ZT value ( 0.4 at 900 °C), sintered at 1450 °C, attributed to enhanced electrical conductivity and a moderate Seebeck coefficient. Notably, this ZT value is the highest reported in the literature for the BaTiO 3 family. Analysis of the correlation matrix emphasized the positive impact of Ta doping on electrical conductivity and its adverse effect on the Seebeck coefficient. These trends were also confirmed by multivariate linear regression provided a large positive coefficient of Ta doping on electrical conductivity while showing a large negative fitting coefficient for the Seebeck coefficient.